Jennifer Lopez is leaving American Idol with big shoes to fill now that she's finally confirmed she won't be back for season 12 -- a decision the 42-year-old singer didn't make lightly.

Confirming her exit to Idol host Ryan Seacrest Friday -- one day after fellow judge Steven Tyler announced his departure -- was a calculated move on Lopez's part, as the singer tells Good Morning America it was Tyler, 64, who cemented her decision to finally move on.

"We had magic," Lopez told ABC News' Amy Robach in a Sunday interview. "I don't know, with him gone, it might be a different formula."

On Thursday, the Aerosmith rocker said that he'd be leaving Idol to return to his performance roots, and Lopez says she'll use her added free time to do the same, intending to finish out her 19-city summer concert tour with Enrique Iglesias before taking on additional film projects -- not to mention tending to her twins, Max and Emme, 4.

Telling Good Morning America she'd welcome the opportunity to appear on Idol in the future, Lopez has high hopes for the talent who will succeed her and Tyler on the judges' panel. "I think like Bono or Bon Jovi or Mick Jagger," she told ABC News. "You know me, I think big."

Late last week, a source told Us WeeklyMariah Carey is among the big names in contention for a seat alongside Randy Jackson, Idol's only remaining original judge.